hfs: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from hfs.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/hfs/mdb.c

@@ -236,10 +236,10 @@ out:
  * hfs_mdb_commit()
  *
  * Description:
- *   This updates the MDB on disk (look also at hfs_write_super()).
+ *   This updates the MDB on disk.
  *   It does not check, if the superblock has been modified, or
  *   if the filesystem has been mounted read-only. It is mainly
- *   called by hfs_write_super() and hfs_btree_extend().
+ *   called by hfs_sync_fs() and flush_mdb().
  * Input Variable(s):
  *   struct hfs_mdb *mdb: Pointer to the hfs MDB
  *   int backup;